The objective of this project is to apply tissue culture techniques to determine the role played by the mouse mammary tumor virus (MuMTV) in the neoplastic transformation of the mammary cell. Experimental inoculation of milk cells, cat cells and C57 BL normal mammary cells with MuMTV induces antigenic changes of the cell surface which can be measured and compared with the surface antigens of normal cells and spontaneous mammary tumors. Efforts are specifically directed to the identification of a tumor antigen which should be distinct from the virus antigen. Human breast tumor cells now available, have shown a low susceptibility to infection by MuMTV in vitro. These cells will be used in attempts to confirm a possible correlation between the mechanisms of mammary carcinogenesis in the mouse and human breast cancer. BIBLIOGRAPHIC REFERENCES: Lasfargues, E. Y.; Lasfargues, J. C.; Dion, A.; Greene, A. E. and Moore, D. H. Experimental infection of a cat kidney cell line with the mouse mammary tumor virus. Cancer Research 36: 67-72, 1976. Lasfargues, E. Y. and Sheffield, J. B. Infectivity and oncogenicity of the mouse mammary tumor virus in tissue culture. J. de Micr. et Biol. Cellulaire. 26:29-34, 1976.